1. Field of the Invention
The present invention relates to a pinch roller device used in a magnetic recording and reproduction apparatus such as a video tape recorder.
2. Description of the Related Art
Recently, there has been a strong demand for more compact, lightweight and lower-cost video tape recorders integrated with cameras. In order to fulfill such demand, it is important to improve the structure of a tape driving device which is included in such recorders and that includes a pinch roller device.
FIG. 15 is a cross-sectional view of a conventional pinch roller device 150. The pinch roller device 150 includes a rotatable capstan shaft 1, a metal sleeve 22, an elastic member 3 formed of rubber, for example, and fixed on an outer circumferential surface of the metal sleeve 22, and a bearing 11 having collars 13. The bearing 11 and the sleeve 22 are integrated together by the collars 13 being pressure-inserted into an inner circumferential surface of the sleeve 22. The pinch roller device 150 further includes a pinch roller shaft 5 for rotatable supporting the bearing 11, and a pinch arm 9 for carrying the pinch roller shaft 5 projecting therefrom. The bearing 11 has an effective bearing face 12 for receiving a force from the pinch roller shaft 5 applied in a radial direction of the pinch roller shaft 5. The bearing 11, the metal sleeve 22, the collars 13 and the elastic member 3 form an assembly 50. The pinch roller shaft 5 is provided therearound with a first position restriction member 7 having a restriction surface 7a for restricting movement of the elastic member 3 in an upward thrust direction (arrow N), and a second position restriction member 8 having a restriction surface 8a for restricting movement of the elastic member 3 in a downward thrust direction (arrow N). Reference numeral 10 represents a tape used for data recording and reproduction.
In the pinch roller device 150 having the above-described structure, the tape 10 runs at a prescribed speed by putting the tape 10 into pressure-contact with the capstan shaft 1 by the elastic member 3 while rotating the capstan shaft 1.
In order to stably run the tape 10, the elastic member 3 needs to press the tape 10 uniformly toward the capstan shaft 1, preferably in the state where the capstan shaft 1 and the pinch roller shaft 5 are parallel to each other. However, for reasons related to the production process, it is inevitable that the pinch roller shaft 5 slightly inclines with respect to the capstan shaft 1. Therefore, it is difficult to dispose the pinch roller shaft 5 and the capstan shaft 1 completely parallel to each other.
FIG. 16 is an enlarged partial view of the pinch roller device 150, illustrating the pinch roller shaft 5 and the vicinity thereof. As shown in FIG. 16, the pinch roller shaft 5 and the effective bearing face 12 of the bearing 11 have a gap therebetween having a size LD in a radial direction of the bearing 11. Using this gap, the elastic member 3 is inclined with respect to the assembly 50 (FIG. 15), so that the pinch roller shaft 5 is parallel to the capstan shaft 1. More specifically, a rotation center line 11a of the bearing 11 is inclined with respect to a rotation center line 5a of the pinch roller shaft 5 at angle xcex8 in a direction in which the elastic member 3 presses the tape 10 toward the capstan shaft 1 (represented by arrow M). In this manner, the elastic member 3 can uniformly pressure the tape 10 toward the capstan shaft 1. Herein, the direction of arrow M is also referred to as a xe2x80x9ctape thickness directionxe2x80x9d.
The conventional pinch roller device 150 has the following problems.
(1) When the size LD of the gap between the effective bearing face 12 and the pinch roller shaft 5 is larger, the freedom in angle xcex8 is also larger. This is preferable in order to accommodate an error in the angle of inclination of the pinch roller shaft 5 with respect to the capstan shaft 1 caused in the production process and thus guarantee stable running of the tape 10.
However, when the size LD is too large, the angle of inclination of the rotation center line 11a with respect to the rotation center line 5a in a tape running direction (perpendicular to the sheet of FIG. 16) is also increased. This is undesirable for the following reason. In general, when the running direction of the tape 10 is changed from forward to reverse or from reverse to forward, the direction of inclination of the elastic member 3 with respect to the capstan shaft 1 is reversed. Where the angle of inclination of the rotation center line 11a (i.e., the angle of inclination of the elastic member 3) with respect to the rotation center line 5a in the tape running direction is too large, the height of the tape 10 with respect to the surface of the capstan shaft 1 rapidly changes when the running direction of the tape 10 is changed. This can damage the tape 10 or cause unstable running of the tape 10. Therefore, in the running direction of the tape 10, the size LD of the gap preferably has a minimum possible size.
Accordingly, the size LD of the gap needs to be appropriately set so that the angle of inclination of the rotation center line 11a with respect to the rotation center line 5a in both of the above-mentioned two directions, is in a range which guarantees stable running of the tape 10. In order to satisfy such contradicting requirements, the variation in the size LD needs to be reduced and an effective length LB of the effective bearing face 12 in the thrust direction needs to be sufficiently large.
In order to reduce the variation in the size LD, the size precision of the components of the pinch roller device 150 needs to be strictly controlled. In addition, when the effective length LB is larger, the distance from the center of the effective bearing surface 12 in the thrust direction to the contact point between the pinch roller shaft 5 and the effective bearing face 12 is longer. This makes it difficult to put the elastic member 3 into uniform pressure-contact with the capstan shaft 1. This is also undesirable to guarantee stable running of the tape 10.
(2) The collars 13 are required in order to secure the bearing 11 inside the sleeve 22. Since the collars 13 need to be reduced in thickness in order to reduce the size of the pinch roller device 150, the collars 13 are usually formed of metal. When the metal collars 13 are pressure-inserted into an inner circumference of the sleeve 22, the collars 13 may undesirably become fixed in the thrust direction while being in contact with the bearing 11. In this state, the collars 13 may deform the bearing 11.
(3) As shown in FIG. 15, the assembly of the pinch roller shaft 5, the first position restriction member 7 and the second position restriction member 8 has a stepped structure. The restriction surface 8a, which is slidably engaged with the bearing 11, needs to be highly smooth in order to reduce friction resistance upon the bearing 11. However, due to the stepped shape of the assembly, the restriction surface 8a cannot be smoothed by a low-cost smoothing technique, such as, for example, centerless polishing. This increases the production cost of the pinch roller shaft 5.
A pinch roller device for putting a tape into pressure-contact with a capstan shaft for running the tape includes a hollow cylindrical elastic member rotating while the tape is running; a sleeve provided on an inner surface of the elastic member for holding the elastic member; a bearing integrated with the sleeve; a pinch roller shaft inserted through the bearing for rotatably supporting the bearing: an inclination restriction member integrated with the pinch roller shaft for restricting an angle of inclination of the pinch roller shaft with respect to the elastic member; a first position restriction member integrated with the pinch roller shaft to be inside the elastic member for restricting a position of the elastic member in a first thrusting direction of the elastic member; a second position restriction member integrated with the pinch roller shaft to be inside the elastic member for restricting a position of the elastic member in a second thrusting direction of the elastic member; and a sliding restriction member integrated with the sleeve and having a circular cross-section along a plane perpendicular to a rotation center line of the elastic member. The bearing has an effective bearing face in contact with an outer circumferential surface of the pinch roller shaft for receiving a force applied from the pinch roller shaft in a radial direction of the pinch roller shaft. The sliding restriction member is disposed at a different portion from the effective bearing face. When an angle between the rotation center line of the elastic member and a rotation center line of the pinch roller shaft approaches a prescribed value, the sliding restriction member contacts the inclination restriction member.
Therefore, the angle between the rotation center line of the elastic member and the rotation center line of the pinch roller shaft can be maintained in a prescribed range.
In one embodiment of the invention, one of the first position restriction member and the second position restriction member is integrated with the inclination restriction member.
In one embodiment of the invention, the inclination restriction member is formed of a resin material and pressure-inserted into the pinch roller shaft.
Therefore, the inclination restriction member can be produced easily and at low cost.
In one embodiment of the invention, the sliding restriction member has a cylindrical inner surface, the inner surface having a roughness equal to or less than 3 xcexcm, and is pressure-inserted into the sleeve.
Therefore, the sliding restriction member can be produced easily and at low cost.
In one embodiment of the invention, the inclination restriction member is produced of an identical material as that of the pinch roller shaft as a result of partially enlarging the diameter of the pinch roller shaft.
In one embodiment of the invention, the pinch roller shaft projects from a pinch arm for supporting the pinch roller shaft, and a portion of the pinch arm acts as the inclination restriction member.
In one embodiment of the invention, the pinch arm is formed of a resin material, and the inclination restriction member is formed integrally with and of the same resin material.
Therefore, the inclination restriction member can be produced easily and at low cost.
In one embodiment of the invention, a cross-section of the inclination restriction member along a plane perpendicular to a rotation center line of the pinch roller shaft has a portion which extends radially outward from a perfect circle, and the portion extending radially outward is contactable with the sliding restriction member.
Therefore, the angle between the rotation center line of the bearing and the rotation center line of the pinch roller shaft can be adjusted in accordance with the angle of inclination of the bearing.
In one embodiment of the invention, xcex8A greater than xcex8S where xcex8A is an angle between the rotation center line of the elastic member and the rotation center line of the pinch roller shaft in a tape thickness direction when the inclination restriction member contacts the sliding restriction member, and xcex8S is an angle between the rotation center line of the elastic member and the rotation center line of the pinch roller shaft in a tape running direction when the inclination restriction member contacts the sliding restriction member.
Therefore, the angle between the rotation center line of the bearing and the rotation center line of the pinch roller shaft when the inclination restriction member contacts the sliding restriction member in the tape thickness direction can be set to a maximum possible value, and the above-mentioned angle in the tape running direction can be set to a minimum possible value, separately from the angle in the tape thickness direction.
In one embodiment of the invention, the bearing is pressure-inserted into the sleeve so as to be fixed.
Therefore, the bearing can be produced easily and at low cost.
In one embodiment of the invention, the elastic member is engaged with the sleeve and held by projections provided along top and bottom perimeters of the sleeve so as not to come off from the sleeve.
Therefore, the sleeve and the elastic member can be integrated easily and at low cost.
In one embodiment of the invention, the sleeve and the bearing are integrated together and formed of an identical material.
Therefore, the sleeve and the bearing can be integrated easily and at low cost.
In one embodiment of the invention, LB less than 0.3 LG where LB represents a length of the effective bearing face in the direction of the rotation center line of the elastic member and LG represents a length of the elastic member in the direction of the rotation center line of the elastic member.
Therefore, the tape can run stably.
Thus, the invention described herein makes possible the advantages of providing a highly reliable pinch roller device providing high performance for stably running the tape.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.